Reflectance characteristics in the submillimeter and millimeter wavelength region of a vacuum compatible absorber

The reflectance characteristics of a grooved sample of Corning Macor, a glass ceramic, were studied in the range 60–1100 GHz for incident and reflected angles ranging from 10° to 65°. Measurements indicate a low, <1%, reflectance for near normal angles of incidence, where the angles of incidence and reflection are defined with respect to a direction normal to the sample face as if it were a planar surface. Higher values, up to 6%, were obtained for other angles of incidence and these results depend upon the orientation of the sample grooves with respect to the polarization of the electric field of the incoming radiation. Structure in the spectra indicates complex interference effects in some configurations.